Since you called the problem “trivial,” we can now all depend on you to resolve these problems for us at little cost, correct?

Restricting arbitrary east-west traffic should be table stakes... It should be the default and you opt into services being able to reach each other. So in that sense its already done.

The solution requires AWS since the gp thinks that's the only access control mechanism that matters. So I doubt there is going to be little cost about it.